This invention relates to a process plant utilising the heat produced by a nuclear reactor in an endothermic chemical process and aims to provide an improved plant layout. One such process is an endothermic reformer process, such as methane/steam reforming to produce hydrogen for example. Advantage is seen in using the high temperature gas from a HTGC reactor to supply process heat. Difficulties arise however in absorbing the substantial amount of heat, produced centrally in the reactor in the characteristically dispersed process zones of the process plant being supplied.